1. Field of the Invention
This invention relates to illumination systems for projection devices and, in particular, relates to scrolling color sequential projection devices, e.g., scrolling color sequential projection devices employing liquid crystal panels.
2. Description of the Prior Art
Color sequential systems are widely used in the projection industry. Every single chip DLP projector has a color wheel, which is commercially available as an off-the-shelf unit. Typically, the color wheel is located at the hot spot of the lamp where the size of the light spot is the smallest. This location provides the fastest color change for the entire panel.
Liquid crystal displays and, in particular, LCoS displays cannot operate as fast as DLP displays. This slower operation is associated with the liquid crystal relaxation time and leads to a significant reduction of projection system efficiency. To increase the light efficiency of the system, it has been suggested to change colors not frame by frame but row by row. This progressive row-at-a-time way of operating a color sequential system substantially doubles the light output.
One example of the application of color sequential illumination to a projection device employing a liquid crystal panel appears in U.S. Pat. No. 6,266,105 B1 (the ""105 patent), which was published as EPO Patent Publication No. EP 0 977 422 A2 on Feb. 2, 2000.
In contrast to the present invention, the system disclosed in the ""105 patent employs reflective, as opposed to transmissive, color filters. As discussed in Brennesholtz, Matthew S., xe2x80x9cColor-Sequential LCoS Projector with a Rotating Drumxe2x80x9d, SID 2002, Paper 51.4, pp. 1346-1349, 2002, reflective color filters of the type disclosed in the ""105 patent suffer from poor efficiency and colorimetry.
In view of the foregoing, the present invention is directed to providing color sequential illumination systems (color scanning systems) which are capable of scrolling bands of colored light across the surface of a panel, e.g., across the surface of a liquid crystal panel such as a LCoS panel. In particular, the present invention is directed to providing scrolling illumination systems which are simple to construct and operate and which achieve sufficiently high levels of color separation between color bands to produce high quality projected images.
In accordance with a first aspect, the invention provides apparatus for producing scrolling bands of colored light (e.g., bands 25 and 27 in FIG. 3) comprising:
(a) an assembly (13) adapted to be rotated about an axis (37), said assembly comprising a plurality of transmissive color filters (e.g., 30, 31, 33) which extend along the axis and define an internal volume (49), a periphery (45), and two opposing ends (47); and
(b) a reflecting surface (39) located at least partially within the internal volume (49) for receiving light which has passed through the periphery (45) and reflecting said light out of one of said ends (47), said reflecting surface (39) being adapted to remain stationary as the assembly (13) rotates about the axis.
In accordance with other aspects, the invention provides a scrolling method comprising:
(a) providing a plurality of color filters (e.g., 30, 31, 33), each filter producing transmitted light from received light;
(b) repetitively passing the filters in front of a light source (e.g., 15, 17) by transporting the filters in a substantially circular path about a rotation axis (37), said light source having an optical axis (41) which is substantially perpendicular to said rotation axis (37); and
(c) turning the optical axis of the transmitted light produced by the filters so that said axis (43) does not pass through a filter.
Additional features and advantages of the invention are set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.